(i) Field of the Invention
This invention relates generally to furnaces and particularly to cooling a motor that drives a draft inducing fan in a furnace. The invention provides for an improved method of cooling the motor that drives the fan and an apparatus for practicing the method.
(ii) Description of the Related Art
Typically, fans driven by an electric motor are used to induce an air flow in a furnace. These fans are designed to produce a certain amount of air flow which is used to remove the products of combustion in a gas-fired furnace and provide a flow of heated air through a heat exchanger. The air flow induced by these fans does not come in contact with the motor and therefore, does not contribute to the cooling of the motor nor dissipation of the heat generated by the motor.
in typical prior art furnaces, the fan motor is located in the vestibule of the furnace which also houses the electronics and controls for controlling the furnace. The heat generated by the blower motor elevates the temperature within the vestibule. The elevated temperature within the vestibule can shorten the life of the electronics and controls located within the vestibule. Additionally, the excess heat generated by the motor can shorten the life of the motor itself.
Typical prior art furnace fans utilize a motor that has an auxiliary fan attached to the rotating shaft of the motor to cool the motor. The auxiliary fan forces a flow of air to flow across the motor to dissipate the heat generated by the motor. An auxiliary fan, however, has many disadvantages.
One disadvantage is that the auxiliary fan increases the size or height of the motor assembly thereby preventing the streamlining of the motor assembly and the associated furnace within which the motor assembly is used. Another disadvantage is that the use of an auxiliary fan produces an additional load on the motor which can reduce the overall motor efficiency and increase the energy consumption of the furnace in which is it used. Furthermore, the use of an auxiliary fan increases the cost of providing the draft inducing fan. Another disadvantage is that the auxiliary fan can generate additional noise which may require the furnace within which it is used to incorporate additional sound deadening techniques. Finally, because the motor is typically used in a vestibule, the air flow induced by the auxiliary fan is channeled into the vestibule thereby contributing to the elevated temperature of the vestibule and the associated components residing therein.
Therefore, it is an object of the present invention to provide an apparatus and method for cooling the motor that eliminates the need for an auxiliary fan.